fc3h: ImportSettings backup_* knobs + alembic 0018 (nightly-enabled, hour, keep-N per kind)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

alembic/versions/0018_fc3h_backup_settings.py

@@ -0,0 +1,62 @@
+"""fc3h: backup_* knobs on import_settings
+
+Revision ID: 0018
+Revises: 0017
+Create Date: 2026-05-24
+
+Adds four columns to the singleton import_settings row:
+  - backup_db_nightly_enabled (default False — opt-in)
+  - backup_db_nightly_hour_utc (default 3)
+  - backup_db_keep_last_n (default 14)
+  - backup_images_keep_last_n (default 3)
+
+server_default ensures the singleton row is backfilled in place
+without an UPDATE statement.
+"""
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+
+revision: str = "0018"
+down_revision: Union[str, None] = "0017"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "import_settings",
+        sa.Column(
+            "backup_db_nightly_enabled", sa.Boolean(),
+            nullable=False, server_default=sa.false(),
+        ),
+    )
+    op.add_column(
+        "import_settings",
+        sa.Column(
+            "backup_db_nightly_hour_utc", sa.Integer(),
+            nullable=False, server_default="3",
+        ),
+    )
+    op.add_column(
+        "import_settings",
+        sa.Column(
+            "backup_db_keep_last_n", sa.Integer(),
+            nullable=False, server_default="14",
+        ),
+    )
+    op.add_column(
+        "import_settings",
+        sa.Column(
+            "backup_images_keep_last_n", sa.Integer(),
+            nullable=False, server_default="3",
+        ),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("import_settings", "backup_images_keep_last_n")
+    op.drop_column("import_settings", "backup_db_keep_last_n")
+    op.drop_column("import_settings", "backup_db_nightly_hour_utc")
+    op.drop_column("import_settings", "backup_db_nightly_enabled")

backend/app/models/import_settings.py

@@ -49,3 +49,17 @@ class ImportSettings(Base):
     download_failure_warning_threshold: Mapped[int] = mapped_column(
         Integer, nullable=False, default=5
     )
+
+    # FC-3h backup knobs.
+    backup_db_nightly_enabled: Mapped[bool] = mapped_column(
+        Boolean, nullable=False, default=False,
+    )
+    backup_db_nightly_hour_utc: Mapped[int] = mapped_column(
+        Integer, nullable=False, default=3,
+    )
+    backup_db_keep_last_n: Mapped[int] = mapped_column(
+        Integer, nullable=False, default=14,
+    )
+    backup_images_keep_last_n: Mapped[int] = mapped_column(
+        Integer, nullable=False, default=3,
+    )